Aluminum polymer capacitor with enhanced internal conductance and breakdown voltage capability

ABSTRACT

An improved capacitor is provided. The capacitor comprises a working element wherein the working element comprises an anode comprising a first dielectric on the anode, a cathode and a conductive separator between the first dielectric and cathode. The conductive separator comprises a separator and a first conductive polymer wherein the first conductive polymer at least partially encapsulates the separator. A second conductive polymer at least partially encapsulates the first conductive polymer and wherein the first conductive polymer has a higher conductivity than the second conductive polymer. An anode lead is in electrical contact with the anode and a cathode lead is in electrical contact with the cathode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a divisional application of pending U.S. patentapplication Ser. No. 16/558,500 filed Sep. 3, 2019 which is incorporatedherein by reference.

BACKGROUND

The present invention is related to capacitors comprising a solidconductive polymeric electrolyte and an optional liquid electrolyte.More specifically, the present invention is related to a capacitorcomprising a conductive separator and a method of forming the hybridcapacitor with improved conductive polymer coverage within theinterstitial portions of a wound structure.

Capacitors have historically been defined within two general types withone type utilizing a liquid electrolyte and the other type utilizing asolid electrolyte. Liquid electrolyte capacitors, generally, comprise alayered structure typically as a winding with an anode conductor, acathode conductor and an interleaved separator immersed in a liquidelectrolyte all sealed within a container. Solid electrolyte capacitors,generally, include a conductive monolith or foil with a dielectric layerthereon and a solid cathode, such as conductive polymer or manganesedioxide, on the dielectric. Both general types of capacitor haveexperienced wide spread use in commerce and each has advantages, anddisadvantages, not common to the other. For example, liquid electrolyticcapacitors have a high capacitance and are capable of high voltages buthave a poor Equivalent Series Resistance (ESR) due to poor conductivityof the electrolyte which is typically not above about 0.015 S/cm.Conductive polymers have a high conductivity, up to 600 S/cm, andtherefore capacitors utilizing conductive polymeric cathodes have a muchlower ESR.

Conductive polymeric cathodes have seen wide spread use in commerce due,at least in part, to their low equivalent series resistance (ESR) andnon-destructive failure mode. This leads to a desire to form a hybridcapacitor wherein the conductive polymers commonly employed for solidelectrolytic capacitors are utilized within the windings of a liquidelectrolyte structure with the goal of achieving the high capacitanceand high voltage common with liquid electrolyte capacitors whilemaintaining the lower ESR common with solid conductive polymericelectrolytes. U.S. Pat. Nos. 8,462,484 and 8,767,377 teach exemplaryhybrid capacitors.

The formation of a hybrid capacitor has typically involved the formationof the interleaved wound structure; comprising anode, cathode andseparator; followed by impregnation with the conductive polymer. Theimpregnation has been done by either in-situ polymerization of monomers,or by diffusion of pre-formed polymer slurry into the interstitial areasof the wound interleaved structure.

In-situ polymerization of a monomer in the presence of an oxidizer wasused to manufacture a first generation of hybrid capacitors. In-situpolymerization is a complex method with many problems includingcontamination of the final product by monomer and oxidizer and the workenvironment conditions are complex leading to poor process reliabilityespecially if the in-situ polymer is applied to the winding. Theseissues were mitigated by the use of water-based dispersions, orslurries, of pre-formed conductive polymer to impregnate theinterstitial spaces of the capacitor winding.

An improvement in hybrid capacitors is presented in commonly assignedU.S. Pat. No. 10,068,713 wherein the polymer layers are formed prior towinding thereby eliminating the problems associated with poor migrationinto the interstitial areas of the winding. While advantageous, thepolymer layers are adjacent, not continuous, which limits theconductivity of the conductive layer.

In spite of the ongoing efforts, those of skill in the art are desirousof an improved hybrid capacitor and method of making an improved hybridcapacitor. The present invention provides a method for making a hybridcapacitor and which exhibits improved electrical quality andreproducibility.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved method forforming a hybrid capacitor and an improved capacitor formed by theimproved method.

A particular advantage is the ability to provide a hybrid capacitor withimproved electrical performance, particularly both higher breakdownvoltage capability, and improved conductivity of the conductive polymerportion of the capacitor.

These and other advantages, as will be realized, are provided in acapacitor comprising a working element wherein the working elementcomprises an anode comprising a first dielectric on the anode, a cathodeand a conductive separator between the first dielectric and cathode. Theconductive separator comprises a separator and a first conductivepolymer wherein the first conductive polymer at least partiallyencapsulates the separator. A second conductive polymer at leastpartially encapsulates the first conductive polymer and wherein thefirst conductive polymer has a higher conductivity than the secondconductive polymer. An anode lead is in electrical contact with theanode and a cathode lead is in electrical contact with the cathode.

Yet another embodiment is provided in a method for forming a capacitor.The method comprises:

forming a working element by:

providing an anode comprising a first dielectric and an anode lead;

providing a cathode comprising a cathode lead;

forming a conductive separator comprising a separator and a firstconductive polymer wherein the first conductive polymer at leastpartially encapsulates the separator;

winding the anode and cathode with the conductive separator between thefirst dielectric and cathode to form a wound capacitor precursor; and

introducing a second conductive polymer into the wound capacitorprecursor wherein the second conductive polymer at least partiallyencapsulates the first conductive polymer

FIGURES

FIG. 1 is a partially unwound schematic perspective view of anembodiment of the invention.

FIG. 2 is a cross-sectional schematic view taken along line 2-2 of FIG.1.

FIG. 3 is a schematic representation of an embodiment of the invention.

FIG. 4 is a schematic representation of an embodiment of the invention.

FIG. 5 schematically illustrates an embodiment of the invention iscross-sectional view.

FIGS. 6 and 7 demonstrate the advantages of the invention graphically.

DESCRIPTION

The instant invention is specific to a capacitor, comprising a solidconductive polymer electrolyte and an optional liquid electrolyteinterspersed in a wound capacitor comprising interleaved anode, cathodeand conductive separator. More specifically, the present invention isdirected to a capacitor, and a method of making a capacitor whichexhibits improved quality. More specifically, the instant inventionallows for the manufacture of capacitors with enhanced performance andspecifically high breakdown voltage and/or lower ESR.

An element of the instant invention is the utilization of a conductiveseparator comprising a first conductive polymer layer a separatorwherein the first conductive polymer layer is at least partially encasedin a second conductive polymer layer which is applied after winding. Thesecond conductive polymer layer extends from the dielectric to thecathode and forms a, preferably continuous, conductor layer from thedielectric to the cathode with the first conductive polymer layer atleast partially encased therein. By incorporating two conductive polymerlayers synergistic improvements can be achieved in conductivity therebyimproving capacitor performance.

In a particularly preferred embodiment the first conductive polymerlayer is formed by in-situ techniques. In-situ formed polymers have ahigher conductivity than those formed separately and then applied as apre-formed polymer. Pre-formed polymers are typically applied as aslurry comprising either particles of conductive polymer or solubilizedpolymer particles. Preformed conductive polymers have a high breakdownvoltage capability. The combination provides a hybrid capacitor whereinthe synergism of the different layers provides a hybrid capacitor with ahigh breakdown voltage capability and a low equivalent series resistance(ESR). Low ESR improves the ripple current capability of the capacitor.

The invention will be described with reference to the various figuresforming an integral non-limiting component of the disclosure. Throughoutthe disclosure similar elements will be numbered accordingly.

An embodiment of the invention will be described with reference to FIG.1 wherein a working element is shown in schematic partially unwound viewprior to insertion into a container and optionally, but preferably,impregnation with liquid electrolyte. In FIG. 1, the working element,generally represented at 10, comprises an anode, 12, and cathode, 14,with a conductive separator, 16, there between. The conductive separatorhas a first conductive polymer, 18, either coated on the separator orthe separator is impregnated, and preferably saturated, with conductivepolymer. An anode lead, 20, and cathode lead, 22, extend from the woundcapacitor and ultimately form the electrical connectivity to a circuit.It would be understood from the description that the anode lead is inelectrical contact with the anode and the cathode lead is in electricalcontact with the cathode and electrically isolated from the anode oranode lead. Tabs, 24 and 26, are commonly employed to electricallyconnect the anode lead to the anode and the cathode lead to the cathodeas known in the art. A closure, 28, such as an adhesive tape inhibitsthe working element from unwinding during handling and assembly afterwhich the closure has little duty even though it is part of the finishedcapacitor.

A cross-sectional view, taken along line 2-2 of FIG. 1, is illustratedschematically in FIG. 2. In FIG. 2, the separator, 16, is shown withconductive polymer, 18, on either side thereof for the purposes ofillustration with the understanding that the separator may beimpregnated, and preferably saturated, with conductive polymer such thatthe dimension of the separator is not appreciably altered by theinclusion of conductive polymer. The anode, 12, and cathode, 14, are ina sandwiched relationship separated by the separator, 16. The separatoris preferably porous with, optional but preferred, liquid electrolytemoving freely through the separator.

An embodiment of the invention will be described with reference to FIG.3 wherein a portion of a wound capacitor is illustrated incross-sectional schematic view. In FIG. 3, the anode, 12, and cathode,14, have a dielectric, 20, and separator layer, 22, there between whichforms a capacitive couple. Only one capacitive couple is illustratedherein with the understanding that the wound capacitor would haveinterleaved and repeating combinations of anode/dielectric/separatorlayer/dielectric. The separator layer comprises a separator which in oneembodiment comprises interwoven fibers, 24. The separator is at leastpartially, and preferably completely, encapsulated in the firstconductive polymer, 18. The first conductive polymer layer is formedfrom a slurry comprising pre-polymerized polymer or by in-situpolymerization. In-situ polymerization techniques to form a conductiveseparator are preferred. A second conductive polymer, 26, introducedafter winding as will be discussed further herein, forms an electricallyconductive path from the dielectric to the first polymer layer to thecathode and at least partially, and preferably completely, encapsulatesthe first conductive polymer. The second conductive polymer ispreferably formed by the introduction of a pre-formed conductive polymerwithout limit thereto. An optional, but preferred, liquid electrolyte,28, at least partially, and preferably completely, fills allinterstitial areas of the separator.

It is preferred that the first conductive polymer layer, 18, be moreconductive than the second conductive polymer, 26. More preferably, theconductivity of the first conductive polymer is at least 150% to no morethan 2500% of the conductivity of the second conductive polymer. By wayof non-limiting example, if the second conductive polymer has aconductivity of 40 S/cm the first conductive polymer has a conductivityof at least 60 S/cm to no more than 1000 S/cm. The average particle sizeof the first conductive polymer is preferably higher than the averageparticle size of the second conductive polymer.

It is preferable that the breakdown voltage of the second conductivepolymer is higher than the breakdown voltage of the first conductivepolymer when measured independently, in identical fashion, either afterinitial formation or after a temperature stress such as 1000 hours at125° C. More preferably, the breakdown voltage of the second conductivepolymer is at least 20% higher to no more than 700% higher than thebreakdown voltage of the first conductive polymer.

It is preferable that the work function of the second conductive polymeris higher than the work function of the first conductive polymer. Morepreferably, the work function of the second conductive polymer is atleast 0.2 eV to no more than 1.2 eV higher than the first conductivepolymer. Work function modifiers are well known in the art asexemplified by U.S. Pat. Nos. 10,340,091 and 10,204,743.

An embodiment of the invention will be described with reference to FIG.4 wherein the process of forming the capacitor is illustrated inschematic view. In FIG. 4, a polymer layer, 18, is formed on aseparator, 16, by the application of a slurry comprising preformedconductive polymer or by application of oxidizer and monomer to form apolymer layer on the separator which is referred to in the art asin-situ polymerization. The applicator, 42, for oxidizer and precursoris not particularly limited herein with any acceptable method forforming a polymer by in-situ polymerization techniques suitable fordemonstration of the invention. The formation of the polymer on theseparator can be done as a master roll which is then slit into rolls ofconductive separator at 44 with a width suitable for formation of awound capacitor. The separator can be split prior to polymer formation,however, this is less desirable due to manufacturing conveniences. Alayered rolled structure is formed as known in the art comprising ananode and cathode with the conductive separator there between. Thedielectric can also be further formed, if necessary, at 46. The woundstructure is impregnated with the second conductive polymer preferablyby introduction of a pre-formed polymer to the interstitial portions ofthe winding at 48, followed by drying. In one embodiment the woundstructure impregnated with the second conductive polymer is assembled at50 followed by aging and testing at 52. If a liquid electrolyte is to beincorporated the liquid electrolyte is added at 54, using conventionaltechniques, and the capacitor is assembled at 56 followed by aging andtesting at 58. Assembly includes the incorporation of the capacitor in ahousing and sealing.

The cathode foil, separators and anode foil are typically provided as awide roll and slit to size. The anode foil is preferably etched and adielectric is formed thereon. The dielectric may be formed prior toslitting in which case a subsequent step is desirable to form dielectricon the slit edge. The separator may be treated with a coupling agent, toimprove adhesion between the surface and conductive polymer layer, or toimpart other specific surface behaviors. The conductive separator may bewashed and dried before or after conductive polymer layer formation orimpregnation and the conductive polymer layer formation or impregnationstep may be repeated several times if required. Electrical leads, ortabs, are typically electrically connected to the anode and cathode,preferably prior to cutting to length and the leads may be treated withmasking material to protect them from farther modification and to keepthem ready for welding to capacitor terminals.

The conductive polymer is applied to the separator by any suitablemethod including immersion, coating, and spraying. In immersion theseparator is pulled through a series of baths or vessels with sequentialapplication of monomer and oxidizer in either order. Immersion ispreferred for the separator. Coating and spraying may be done with anyprinting technique including screen printing or spraying of a monomer oroxidizer either sequentially, in any order, or simultaneously onto thesurface of the separator. It is preferable that the conductive polymercoating be applied to the separator at an amount of at least 0.1 mg/cm².Below about 0.1 mg/cm² the coating weight is insufficient for adequateconduction and incomplete coating may result. It is preferable that theconductive polymer coating be applied in an amount sufficient to achievea coating weight of no more than about 10 mg/cm². Above about 10 mg/cm²the added coating thickness does not appreciably increase theconductivity.

Multi-tab or multi-leads minimizes the foil resistance effect and arepreferred. With a single lead the current must flow from the furthestextent of the foil to the tab and lead which is detrimental to ESR. Itis preferable to utilize multiple anode leads and multiple cathode leadsthereby decreasing the conductive path length.

A capacitor is illustrated in cross-sectional schematic view in FIG. 5.In FIG. 5, the capacitor, generally represented at 60, comprises aworking element, 62, as described herein, within a housing, 64. Thehousing, which may be referred to as a can in the art, is preferablyconductive and may function as a lead or be in electrical contact with acathode lead, 6. Cathode tabs, 68, are in electrical contact with thehousing or cathode lead. Anode tabs, 70, are in electrical contact withan anode lead, 72. A lid, 74, and seal, 76, such as a gasket, seals thehousing to inhibit atmospheric exchange between the interior of thehousing and ambient atmosphere. In one embodiment the seal is a hermeticseal.

The anode is a conductive metal preferably in the form of a foil. Theconductive metal is preferably a valve metal or a conductive oxide ofthe valve metal. Particularly preferred anodes comprise a valve metalsuch as tantalum, aluminum, niobium, titanium, zirconium, hafnium,alloys of these elements, or a conductive oxide thereof such as NbO.Aluminum is a particularly preferred anode material.

An oxide film is formed on the anode as the dielectric. The dielectricmay be formed using any suitable electrolyte solution, referred to as aforming electrolyte, such as a phosphoric acid or a phosphate-containingsolution, boric acid, borate containing solution or ammonium adipate. Aformation voltage of from about 9 V to about 450 V is commonly applied.The formation voltage typically ranges from 1.5 to 3.5 times the ratedvoltage of the capacitor.

The conductive polymer application process is generally selected fromin-situ polymer formation and application of a preformed polymer from aslurry such as by a coating process. For the in-situ processimpregnating solutions are applied to the surface wherein theimpregnating solutions preferably contain monomer, oxidizing agent,dopant and other adjuvants as known to those of skill in the art. Theselection of a suitable solvent for the solution is well within thelevel of skill in the art. Examples of suitable solvents include ketonesand alcohols such as acetone, pyridine, tetrahydrofuran, methanol,ethanol, 2-propanol, and 1-butanol. The monomer concentration may befrom about 1.5 wt. % to about 20 wt. %, more preferably from about 5 wt.% to about 15 wt. % for demonstration of the invention. Suitablemonomers for preparing conductive polymers include but are not limitedto aniline, pyrrole, thiophene, and derivatives thereof. A preferredmonomer is 3,4-ethylenedioxythiophene. The oxidizing agent concentrationmay be from about 6 wt. % to about 45 wt. % and more preferably fromabout 16 wt. % to about 42 wt. % for demonstration of the invention.Oxidizing agents for preparing conductive polymers include Fe(III) saltsof organic and inorganic acids, alkali metal persulfates, ammoniumpersulfate, and others. A preferred oxidant for demonstration of theinvention is Fe(III) tosylate. The dopant concentration may be fromabout 5 wt. % to about 30 wt. % and more preferably from about 12 wt. %to about 25 wt. %. Any suitable dopant may be used, such as polystyrenesulfonate, dodecyl benzenesulfonate, p-tosylate, or chloride. Thepreferred dopant is p-tosylate. The substrates are cured at atemperature of from 65° C. to about 160° C. and more preferably fromabout 80° C. to about 120° C. thereby allowing the monomer topolymerize. After curing, the polymer layer is preferably washed indeionized water or another solvent.

Application of a preformed polymer from a slurry after winding is apreferred method for introducing the second conductive polymer into thewinding. The polymer can be prepared as a slurry or obtainedcommercially as a slurry, without particular limit to the technique,preferably followed by drying. A slurry of polymerized3,4-ethylenedioxythiophene doped with polystyrene sulfonate or anothersuitable dopant, with a particle size of no more than 200 nm, preferablyat least 1 nm to no more than 200 nm, more preferably at least 20 nm tono more than 200 nm, in a solvent is exemplary for demonstration of theinvention. A particularly preferred slurry has an indistinguishableparticle size by scatter techniques and is referred to as a solubleconductive polymer

The liquid electrolyte is a solvent preferably with a supporting salttherein. Any conventional solvent can be used with exemplary solventsincluding γ-butyrolactone, sulfolane, ethylene carbonate, propylenecarbonate, dimethyl carbonate, ethyl methyl carbonate, acetonitrile,propionitrile, dimethyl formamide, diethyl formamide, water, siliconeoil, polyethylene glycol and mixtures thereof. Though not required asupporting salt is preferred. Exemplary supporting salts includeinorganic acid ammonium salts, inorganic acid amine salts, inorganicacid alkyl substituted amide salts, organic ammonium salts, organic acidamide salts, organic acid alkyl substituted amide salts and derivativesthereof. Any gas absorbents or cathode electrochemical depolarizers canbe used. Exemplary supported additives include nitro derivatives oforganic alcohols, acids, esters, aromatic derivatives such as o-, m-,p-nitroanisole, o-,m-,p-nitrobenzoic acid, o-,m-,p-nitrobenzene alcohol.A particularly preferred hybrid capacitor comprises up to 50 wt % liquidelectrolyte.

The separator is not particularly limited herein and any commerciallyavailable separator can be used to demonstrate the invention with theproviso that it is a material used for the conductive separator caneither be coated with, or impregnated with, a conductive polymer.Alternatively, or in addition to the conductive polymer, the separatormay itself be a conductive material. Exemplary separators for theconductive separator function as a skeleton layer for the conductivepolymer. The separator can be fabricated in the form of a sheet ofdifferent dimensions which can be wound in rolls. The anode foil canfunction as a support for the separator wherein the anode foil has aninsulator layer formed on the surface thereof with a conductive polymercoating on the insulator and with a conductive separator layer formed onthe polymer coating. The use of the anode as a support may minimizeoperating difficulty. The separator comprises a porous conductive layerwhich allows direct electrical contact between the anode conductivepolymer layer and a cathode. Preferably, the separator has a volume ofpores for liquid electrolyte to transit through. Paper or othernon-conductive materials, such as polymers, can be used as support forthe conductive polymer. Paper is an exemplary separator due to thewidespread use and availability. Unlike prior art capacitors the paperdoes not need to be charred for use as a conductive separator. In themanufacture of prior art capacitors the paper is often charred afterformation of the working element to minimize the amount of polymerabsorbed into the paper. With the present invention this is unnecessarysince the separator is either coated with conductive polymer orimpregnated with conductive polymer to form the conductive separator.The separator may be a fibrous material, such as paper fiber, eitherphysically intermingled or cross-linked to form a continual fibrous,such as paper fiber, layer. The space between the fibers might be partlyor fully filled with the highly conductivity component. Paper basedseparators can be manufactured by modification of a finished paper layeror by modification of paper with high conductivity component fibersbefore forming of paper layer, a dispersion of conductive fibers,pieces, particles or their agglomerates in a liquid or solid state or adeposition of conductive fibers, pieces, particles. The conductivefibers, pieces or particles may comprise a conductive material such asconductive polymer, carbon black, graphite, metal etc., or can be acomposite material consisting of a non-conductive core such as paper,plastic etc., modified with a conductive material such as conductivepolymer, carbon black, graphite, metal etc.

The conductive separator and non-conductive separator may comprise thesame material with the conductive separator having a conductive coatingthereon or being impregnated with a conductor neither of which isnecessary in the non-conductive separator.

A particularly preferred separator has a width which is suitable for theworking element length or production process with a width of 1.5 cm to500 cm being exemplary for demonstration of the invention. The length ischosen based on the desired capacitance as capacitance is a function ofanode and cathode overlap and is therefore directly related to lengthand width of the cathode and anode. A separator with a length of for 0.1m to 400 m and thickness of 10 μm up to 300 μm is exemplary fordemonstration of the invention.

The conductive polymer is preferably selected from polyaniline,polypyrrole and polythiophene or substitutional derivatives thereof.

A particularly preferred conducting polymer is represented by Formula I:

wherein R¹ and R² are chosen to prohibit polymerization at the β-site ofthe ring. It is most preferred that only α-site polymerization beallowed to proceed. Therefore, it is preferred that R¹ and R² are nothydrogen. More preferably, R¹ and R² are α-directors. Therefore, etherlinkages are preferable over alkyl linkages. It is most preferred thatthe groups be small to avoid steric interferences. For these reasons R¹and R² taken together as —O—(CH₂)₂—O— is most preferred. In Formula 1, Xis S, N or O and most preferable X is S. A particularly preferredconductive polymer is polymerized 3,4-polyethylene dioxythiophene(PEDOT).

R¹ and R² independently represent linear or branched C1-C16 alkyl orC2-C18 alkoxyalkyl; or are C3-C8 cycloalkyl, phenyl or benzyl which areunsubstituted or substituted by C1-C6 alkyl, C1-C6 alkoxy, halogen orOR³; or R¹ and R², taken together, are linear C1-C6 alkylene which isunsubstituted or substituted by C1-C6 alkyl, C1-C6 alkoxy, halogen,C3-C8 cycloalkyl, phenyl, benzyl, C1-C4 alkylphenyl, C1-C4 alkoxyphenyl,halophenyl, C1-C4 alkylbenzyl, C1-C4 alkoxybenzyl or halobenzyl, 5-, 6-,or 7-membered heterocyclic structure containing two oxygen elements. R³preferably represents hydrogen, linear or branched C1-C16 alkyl orC2-C18 alkoxyalkyl; or are C3-C8 cycloalkyl, phenyl or benzyl which areunsubstituted or substituted by C1-C6 alkyl. In a particularly preferredembodiment R³ comprised an anionic group with a corresponding cationicgroup wherein Formula I is an intrinsically conductive polymer withoutthe necessity of a counterion which is referred to as a self-dopingpolymer.

As typically employed in the art, various dopants can be incorporatedinto the polymer during the polymerization process. Dopants can bederived from various acids or salts, including aromatic sulfonic acids,aromatic polysulfonic acids, organic sulfonic acids with hydroxy group,organic sulfonic acids with carboxylhydroxyl group, alicyclic sulfonicacids and benzoquinone sulfonic acids, benzene disulfonic acid,sulfosalicylic acid, sulfoisophthalic acid, camphorsulfonic acid,benzoquinone sulfonic acid, dodecylbenzenesulfonic acid, toluenesulfonicacid. Other suitable dopants include sulfoquinone,anthracenemonosulfonic acid, substituted naphthalenemonosulfonic acid,substituted benzenesulfonic acid or heterocyclic sulfonic acids asexemplified in U.S. Pat. No. 6,381,121 which is included herein byreference thereto.

Binders and cross-linkers can be also incorporated into the conductivepolymer layer if desired. Suitable materials include poly(vinylacetate), polycarbonate, poly(vinyl butyrate), polyacrylates,polymethacrylates, polystyrene, polyacrylonitrile, poly(vinyl chloride),polybutadiene, polyisoprene, polyethers, polyesters, silicones, andpyrrole/acrylate, vinylacetate/acrylate and ethylene/vinyl acetatecopolymers.

Other adjuvants, coatings, and related elements can be incorporated intoa capacitor, as known in the art, without diverting from the presentinvention. Mentioned, as a non-limiting summary include, protectivelayers, multiple capacitive levels, terminals, leads, etc.

The inventive capacitor has a rated voltage of at least 15 volts to nomore than 400 volts and more preferably no more than 500 volts whereinrated voltage is approximately 50% of the dielectric formation voltage.

Examples

A cellulose fibers based material with density 0.35 g/cm3, thickness 50um was used as separator and treated with commercially availablepolymerized 3,4-polyethylene dioxythiophene provided as a slurry to forman at least partially encapsulated control conductive separator. Thecontrol separator was dipped in slurry twice, the slurry was driedinitially at 80° C. and then at 150° C. to form a solid coating. Anidentical cellulose fibers separator was treated by immersion in asolution comprising iron tosylate as an oxidizer and, after drying for 3hours at ambient temperatures, in a solution comprising 3,4-ethylenedioxythiophene monomer. Polymerization of the monomer was allowed toproceed for 3 hours at ambient temperature followed by 3 hours at 40° C.to form polymerized 3,4-polyethylene dioxythiophene thereby forming aninventive conductive separator. The inventive conductive separator waswashed in ethanol, dried and cured at for 40° C. for one hour and at125° C. for 3 hours. The resistance of each conductive separator wastested multiple times with the same probe resulting in a resistance of4.6 (±0.44) ohms for the inventive conductive separator and 8.1 (±0.49)ohms for the control conductive separator. The inventive conductiveseparator demonstrated an increase in conductivity improvement of about76% relative to the control.

Three capacitors were made for the purposes of demonstrating theinvention. Each was based on a 720 Vf aluminum foil with a dielectricformed up to 500 V in a boric acid solution after slitting. Capacitor 1was formed by forming an in-situ polymer on the dielectric comprisingpolymerizing 3,4-ethylene dioxythiophene with iron tosylate. Capacitor 2was prepared with the same conductive separator as Capacitor 1 whereinthe a polymer slurry of polymerized 3,4-polyethylene dioxythiophene wasincorporated as the second conductive polymer after assembling.Capacitor 3 was prepared the same as Capacitor 2 except that a highvoltage liquid electrolyte (Vs-450V) was included. The results arepresented in FIGS. 6 and 7. In FIG. 6 the upper trace represents theresult for Capacitor 1 and the lower trace represents the results forCapacitor 3. FIG. 7 represents the results for Capacitor 2.

As shown in FIGS. 6 and 7, for Capacitors 2 and 3, correspond to thescheme presented in FIG. 3, the voltage capability for the prototypeswas higher than 200V. The first spark occurred at 300V for Capacitor 2but the leakage current remained stable and multiple sparks with currentinstability occurred at 400V. For this structure 300V was the limit involtage. The inventive samples demonstrated good leakage currentperformance and multiple failures were observed and detected as currentinstability at 400V. The full in-situ capacitor structure demonstratedthe worse results. First, leakage current was almost 2 orders higher vs.the inventive capacitors even at very low voltages such as 10V-30V. At50V leakage current begun to rise significantly and this can be alreadyconsidered as voltage limit. At 100V Capacitor 2 failed with a shortcircuit failure mode.

The invention has been described with reference to the preferredembodiments without limit thereto. One of skill in the art would realizeadditional embodiments and improvements which are not specifically setforth herein but which are within the scope of the invention as morespecifically set forth in the claims appended hereto.

The invention claimed is:
 1. A method for forming a capacitorcomprising: forming a working element by: providing an anode comprisinga first dielectric and an anode lead; providing a cathode comprising acathode lead; forming a conductive separator comprising a separator anda first conductive polymer wherein said first conductive polymer atleast partially encapsulates said separator; winding said anode and saidcathode with said conductive separator between said first dielectric andsaid cathode to form a wound capacitor precursor; and introducing asecond conductive polymer into said wound capacitor precursor whereinsaid second conductive polymer at least partially encapsulates saidfirst conductive polymer.
 2. The method for forming a capacitor of claim1 wherein said first conductive polymer is formed by in situpolymerization techniques.
 3. The method for forming a capacitor ofclaim 1 wherein said introducing slurry into said wound capacitorprecursor wherein said slurry comprises a pre-formed conductive polymer.4. The method for forming a capacitor of claim 1 wherein said firstconductive polymer has a higher conductivity than said second conductivepolymer.
 5. The method for forming a capacitor of claim 4 wherein saidfirst conductive polymer has a first conductivity and said secondconductive polymer has a second conductivity wherein said firstconductivity is at least 150% to no more than 2500% of said secondconductivity.
 6. The method for forming a capacitor of claim 1 whereinsaid first conductive polymer has a first breakdown voltage and saidsecond conductive polymer has a second breakdown voltage wherein saidsecond breakdown voltage is higher than said first breakdown voltage. 7.The method for forming a capacitor of claim 6 wherein said secondbreakdown voltage is 120% to 700% of said first breakdown voltage. 8.The method for forming a capacitor of claim 1 wherein said firstconductive polymer has a first work function and said second conductivepolymer has a second work function wherein said second work function ishigher than said first work function.
 9. The method for forming acapacitor of claim 8 wherein said second work function is at least 0.2eV to no more than 1.2 eV higher than said first work function.
 10. Themethod for forming a capacitor of claim 1 further comprising: adding aliquid electrolyte to said working element wherein said liquidelectrolyte is between said dielectric and said cathode.
 11. The methodfor forming a capacitor of claim 1 wherein said conductive separator hasa first conductive polymer coating weight of at least 0.1 mg/cm² to nomore than 10 mg/cm2.
 12. The method for forming a capacitor of claim 1wherein said conductive separator comprises a separator with said firstconductive polymer coated on said material or said first conductivepolymer impregnates said separator.
 13. The method for forming acapacitor of claim 12 wherein at least one of said first conductivepolymer or said second conductive polymer comprises a polymer selectedfrom the group consisting of polyaniline, polythiophene and polypyrrole.14. The method for forming a capacitor of claim 13 wherein saidpolythiopene is poly 3,4-ethylenedioxythiophene.
 15. The method forforming a capacitor of claim 13 wherein said first conductive polymer orsaid second conductive polymer is a self-doping polymer.
 16. The methodfor forming a capacitor of claim 1 comprising forming multiple anodeleads or multiple cathode leads.
 17. The method for forming a capacitorof claim 1 wherein at least one of said anode or said cathode comprisesa valve metal.
 18. The method for forming a capacitor of claim 17wherein said valve metal is selected from the group consisting oftantalum, aluminum, niobium, titanium, zirconium, hafnium, alloys ofthese elements and a conductive oxide thereof.
 19. The method forforming a capacitor of claim 18 wherein said valve metal is aluminum.20. The method for forming a capacitor of claim 1 having a rated voltageof at least 15 volts to no more than 500 volts.
 21. The method forforming a capacitor of claim 1 wherein said first conductive polymer hasan average particle size which is higher than an average particle sizeof said second conductive polymer.
 22. The method for forming acapacitor of claim 21 wherein said second conductive polymer is asoluble conductive polymer.
 23. The method for forming a capacitor ofclaim 21 wherein said second conductive polymer has a particle size ofno more than 200 nm.
 24. The method for forming a capacitor of claim 21wherein said particle size is at least 1 nm.
 25. The method for forminga capacitor of claim 24 wherein said particle size is at least 20 nm.